Carriages for transporting sheets of glass through a furnace having a plurality of sheet processing stations where the carriage rides on a rail positioned above the furnace have been previously proposed. Such carriages have included a carrying frame fitted with a longitudinal horizontal member having hangers which project downwardly into the furnace and from which a sheet of glass is adapted to be suspended. An example of such a carriage is described in German Patent Publication No. 2607276.
In order for a sheet of glass to be formed into a convex shape, the furnace is provided with a convexing station including pressing tools mounted on rams where the sheet is suspended from the carriage so as to be positioned between the tools prior to the tools being pressed together to form the sheet into a convex shape. It is important that the sheet be precisely positioned between the tools in order that it may be accurately shaped, and it has been found that the greater the degree of curvature, that the greater is the need for accurate positioning. It has been proposed to include a guide fork on one of the pressing tools to surround and hold one of the clamps connecting the sheet to a hanger to further position the sheet during closing of the pressing tools. Such a device is disclosed in German Pat. No. 1,146,625.
When sheets having great degree of curvature are manufactured, and especially sheets having accentuated bends, as for example sheets which are made in installations such as described in German Pat. No. 2741965, it becomes necessary to position the sheet with respect to the convexing station with the utmost accuracy. This requires that the entire sheet suspension system be accurately positioned since the use of a guide fork alone as described above will not produce the degree of positioning necessary for accurately forming the sheets.
A problem that has existed with prior art devices having carriages for transporting sheets of glass through a furnace is that the carriage framework expands on being heated which can then effect accurate positioning of a sheet at the convexing station. It is known that a carriage 2-3 meters in length may expand in excess of 10 l mm when subjected to high temperatures. This expansion may then result in a shift of the sheet in the convexing station even when the station is equipped with a guide fork as described above.
It is therefore an object of the invention to provide for a device which will accurately position a sheet of glass in a convexing station and which will reduce to a minimum any slight displacement of a sheet that might result from expansion of parts making up the structure supporting the sheet when the structure is subjected to high temperatures.